Manager accusing customer

I bought a headset at The Grove Musica on 11/10/2015 @ 16:12. I told the lady that it was opened before. @ 16:18 I returned to Musica and explained that it was broken. The manager then told me that it is not possible and they do not sell broken items. I explained to her that I only bought it 5 min before and that I told the lady that I thought it was opened before. She kept me there for 20min stating 4 times that she does not understand. I explained to her the CPA and she still refused to help me. I raised my voice as I just spend R400 and bought a broken item. According to Musica it is my problem and I should have checked it.